1. Field of the Invention
This invention relates to optical fibers used in laser treatment applications such as, by way of example and not limitation, benign prostate hypertrophy (BPH) treatments.
The invention replaces a side-firing optical fiber surrounded by a protective end cap with one of the following end-firing optical fiber arrangements:    (i) an end-firing optical fiber having a protective ferrule welded to the optical fiber, the index of refraction of the ferrule being matched to that of the fiber to cause dispersal of laser energy and increase the firing angle of the laser, or    (ii) an end-firing optical fiber and protective ferrule mounted in a cannula, the cannula having a pre-formed curvature that enables treatment of lateral tissues when the cannula is extended out of a scope, but that is sufficiently flexible to enable the cannula to be withdrawn into a scope having a straight working channel.
By directing treatment radiation in an axial or “end-fire” rather than side-firing direction, the thickness or length of the material through which the treatment radiation is directed can be increased without limitation due to the size of the working channel through which the optical fiber and ferrule are inserted.
2. Description of Related Art
FIG. 1A shows a conventional side firing fiber arrangement for surgical applications. The conventional fiber arrangement typically uses a 600 micron fiber 1 having a beveled tip 52 at a distal or exit end of the fiber to reflect laser energy L laterally from the laser axis. The lateral reflection uses principles of total internal reflection. To maintain the total internal reflection in a fluid environment, such as a vein or within the urinary tract, a quartz cap 53 covers the beveled tip.
The quartz cap 53 of the conventional arrangement shown in FIG. 1 typically is limited to a maximum outer diameter OD of 1.8 mm and an internal diameter ID of about 1 mm. This limits the wall thickness of the cap 53 to about 400 microns. During lasing into soft tissue, the surface of the cap begins to erode due to free electron absorption when the temperature of the cap exceeds one thousand degrees in the area through which the laser is directed. This erosion on the surface of the cap scatters the energy, thereby lowering the power density and efficiency of vaporizing tissue.
Normally, the temperature of the end cap 53 will not exceed one thousand degrees during a BPH treatment. However, when contact is made with the tissue being treated, such as prostate tissue during a BPH treatment, the temperature of the cap can rise rapidly, and a hole can appear before the operator is aware of the problem. The fluid migrating through the hole will cause the angle tip to cease functioning and the treatment radiation to instead cause internal heating in the area of the fiber tip. This internal heating not only can damage the fiber tip, it may even cause the cap to explode.
FIGS. 1B and 1C illustrate the erosion process in more detail. In these figures, reference numeral 27 indicates a conventional side fire probe including a side fire fiber 36 having an angled tip 40 enclosed within a fused silica cap 15. Cap 15 extends from a ferrule 35 that is secured to the fiber 36. The angled tip causes treatment radiation to be directed through the cap in an area 16 positioned between the fiber 36 and the tissue to be treated. As with the arrangement illustrated in FIG. 1A, the cap 15 shown in FIGS. 2A and 2B may erode in the area 16 through which the treatment radiation is directed, allowing fluid migration into the cap. Reference numeral 28 indicates the side fire probe 27, after erosion has created a hole 19, permitting ingress of fluid and excessive heating in the vicinity 18 of the tip of fiber 36.
One possible solution to the problem of erosion would be to simply increase the wall thickness of the cap 15. However, such an increase in thickness is not possible for many applications because the overall diameter of the cap 15 is limited by the diameter of the working channel of the scope through which it is extended. As noted above, for example, the maximum diameter of a cap used in BPH treatment is about 1.8 millimeters because the cap is required to fit into the working channel of a cystoscope used in BPH treatment is about 1.8 millimeters.